Stygocapitella subterranea Knöllner, 1934

Struck, Torsten H., Koczula, Jens, Stateczny, Dave, Meyer, Christian & Purschke, Günter, 2017, Two new species in the annelid genus Stygocapitella (Orbiniida, Parergodrilidae) with comments on their biogeography, Zootaxa 4286 (3), pp. 301-332 : 316-322

Species Stygocapitella subterranea Knöllner, 1934

( Figs. 5 , 7 , 8 B)

Stygocapitella subterranea Knöllner, 1934 ; Karling, 1958; Westheide, 1966, 2008; Schmidt, 1969, 1970; Riser, 1980, 1984; Purschke, 1986, 1987, 1999, 2006; Worsfold & Dyer, 1997; Schmidt & Westheide, 2000; Worsfold, 2006; Purschke & Fursman, 2005; Purschke & Jördens, 2007

Types and material examined. Neotype: female, Germany: Schilksee , N 54° 25.432' / E 010° 10.484', high water line + 2 m at a depth of 30–45 cm, coll. Natural History Museum of the University of Oslo ( NHMO C6961). Additional material : Germany: Schilksee , N 54° 25.432' / E 010° 10.484', high water line + 2 m at a depth of 30–45 cm, 2 females, 2 males & 1 immature. coll. Natural History Museum of the University of Oslo ( NHMO C6962). Besides the neotype and mature additional material six specimens for molecular work and two for SEM have examined.

Diagnosis. A broadly rounded prostomium and a peristomium followed by 13 segments of which 10 bear chaetae and a rounded pygidium. The first chaetigerous segment possesses two bilimbate chaetae with a whip-like extension, two bilimbate and two forked chaetae, the second one three bilimbate and two forked chaetae and all following ones two bilimbate and two forked chaetae.

Description. Color: White-transparent with slight iridescence at the surface.

Size: 1.5–2.7 mm, width 200–320 µm (based on literature and results herein).

The body comprises a prostomium without appendages, a peristomium bearing the mouth opening, 13 segments and a round pygidium. 1st to 12th segment biannulated. Chaetae in a pair of ventrolateral bundles are present at segments two to 11 in the first ring of each segment. Two bilimbate chaetae with whip-like extensions are present in the second segment in each bundle. At least two bilimbate and two forked chaetae are present in each bundle of all following segments with chaetae. The third segment has one additional bilimbate chaetae in each bundle. The forked chaetae possess four to six regular teeth between the stronger outer prongs, but these teeth are difficult to determine by light microscopy only. Gonochoristic sexes are present. In males the paired spermioducts open ventrally in segment 10 and in females the genital pores are located at the ventral boundary between the 10th and 11th segment. One or two vitellogenic oocytes can be observed at a time.

Habitat & Distribution: Specimens predominantly occur at beaches with medium-sized sand grains at or above the higher water level up to a depth of 90 cm. Especially at beaches with low tidal exposure specimens might occur substantially above the waterline. Specimens are known from a wide distribution in Europe comprising the Northern Atlantic (Norwegian north coast), the North Sea (English, German, & Swedish west coast), the Baltic Sea (German & Swedish south coast), the Eastern Atlantic Ocean (English & French west coast), the Mediterranean Sea (French & Tunisian coast), and the Black Sea (Romanian coast). Records have also been reported from the Western Atlantic Ocean (Massachusetts, Maine, New Brunswick), the Eastern Pacific Ocean (California, Washington, USA; Vancouver Island, Canada) and New Zealand in the southern hemisphere.

Remarks. No holotypus had been deposited for S. subterranea with its first description based on specimens collected from the beach in Schilksee ( Germany). Additionally, no neotypus in any later description or report has been assigned as well. Therefore, we emend this situation herein by assigning a neotypus for S. subterranea from its type locality in Schilksee ( Germany) as well as several specimens as additional material. Although all segments are reported as being biannulated (e.g., Westheide, 2008) this is obviously not the case for the last segment which comprises only one ring and is only half the size of the proceeding segment. This is in accordance with Karling’s (1958: p. 312) observations.

There is an indication for the presence of several cryptic species in S. subterranea . Especially, populations from the Western Atlantic (i.e., Nahant, Maine) and Eastern Pacific Ocean (i.e., San Juan Island, Washington) are genetically distinct from each other and from a European population (List, Sylt) ( H. Schmidt & Westheide, 2000). Herein the COI datasets also indicated higher genetic differences between the North Sea population from List and the Baltic one from Schilksee. This is congruent with previous results for European populations from the Swedish west coast, the Baltic Sea, the North Sea and the Black Sea exhibiting distinct genetic units albeit given close relationships to each other ( Westheide, 2008).

Additionally, the population from New Zealand originally reported as S. subterranea lacks any description of morphology as well as genetic data so far ( Riser, 1984). Hence, it cannot be securely placed in either S. australis sp. n. or S. subterranea as described herein.

Species Stygocapitella australis , sp. n. ( Figs. 6 , 7 , 8 A)

Stygocapitella subterranea Hartmann-Schröder, 1983 , possibly Riser 1984

Types and material examined. Holotype: male, Australia: Gnarabup Beach , S 33° 59.097' / E 114° 59.421', high water line + 3 m at a depth of 15–30 cm, coll. Western Australian Museum ( WAM V8605).

Paratypes: Australia: Gnarabup Beach, S 33° 59.097' / E 114° 59.421', high water line + 3 m at a depth of 15–30 cm, 2 females & 2 males ; Sarge Bay, S 34° 22.060' / E 114° 08.874', high water line + 4 m at a depth of 15–30 cm, 4 females, 2 males & 3 immature. coll. Western Australian Museum ( WAM V8606 & WAM V8607) & Natural History Museum of the University of Oslo ( NHMO C6957 & NHMO C6958). Besides the holotype and mature paratypes, six specimens from each population for molecular work and three specimens for SEM were examined. Moreover, the original deposits of Hartmann-Schröder in the Zoological Museum Hamburg ( ZMH P-17530 for Gnarabup Beach and ZMH P-17531 for Sarge Bay ) are also elevated to paratypes.

Diagnosis. A broadly rounded prostomium and a peristomium followed by 13 segments of which 10 bear chaetae and a rounded pygidium. Segments 1 to 12 biannulated, segment 13 comprises a single ring only. The first chaetigerous segment possesses two bilimbate chaetae with a whip-like extension, one bilimbate and two forked chaetae, and all following ones two bilimbate and two forked chaetae.

Description. Color: White-transparent with slight iridescence at the surface.

Size: 2.6–3.2 mm, width 250–300 µm (based on results herein).

The body comprises a prostomium without appendages, a peristomium bearing the mouth opening, 13 segments and a rounded pygidium without appendages. 1st to 12th segment biannulated. Chaetae in pairs of ventrolateral bundles are present at segments 2 to 11 in the first ring of each segment. First chaetiger with two bilimbate chaetae with whip-like extensions, two forked chaetae and bilimbate chaeta in each bundle. All following chaetigers possess two bilimbate and two forked chaetae in each bundle. The forked chaetae usually comprise three to four regular teeth between the stronger outer prongs, these teeth are difficult to determine by light microscopy only, at least 100x objective necessary. Gonochoristic. In males the paired spermioducts open ventrally in segment 10 and in females the genital pores are located at the ventral boundary between the 10th and 11th segment. One or two vitellogenic oocytes can be observed at a time.

Habitat & Distribution: Specimens occur at beaches with medium-sized sand grains above the higher water level up to depth of 75 cm. So far only known from the Western Australian coast.

Remarks. As discussed above the New Zealand S. subterranea specimens could possibly either represent S. australis sp. n. as well or be more closely related to S. australis sp. n. than to S. subterranea .

Etymology. The species name australis being Latin for southern refers to its first record from Australia.

Species Stygocapitella minuta , sp. n. ( Figs. 4 , 7 , 8 C)

Types and material examined. Holotype: male, South Africa: Langebaan , S 33° 04.880' / E 018° 01.919', high water line + 6 m at a depth of 30–45 cm. coll. Natural History Museum of the University of Oslo ( NHMO C6959).

Paratypes: South Africa: Langebaan , S 33° 04.880' / E 018° 01.919', high water line + 6 m at a depth of 30–45 cm, 6 females, 4 males & 6 immature. coll. Natural History Museum of the University of Oslo ( NHMO C6960) & Zoological Museum Hamburg ( ZMH P 27823) . Besides the holotype and mature paratypes 14 specimens for molecular work (for most the location was at same beach but at S 33° 04.940'/E 018° 01.859', high water line + 6 m at a depth of 30–45 cm) and six for SEM were examined.

Diagnosis. A broadly rounded prostomium and a peristomium followed by 13 segments of which eight bear chaetae and a forked pygidium. First 12 segments biannulated. The first chaetiger possesses three bilimbate chaetae with a whip-like extension and two bilimbate chaetae, and all following ones four bilimbates; forked chaetae absent.

Description. Color: White-transparent with slight iridescence at the surface.

Size: 1.4–1.6 mm, width 140–180 µm (based on results herein).

The body comprises a prostomium without appendages, a peristomium bearing the mouth opening, 12 biannulate segments, 1 segment consists of a single annulus and a forked pygidium. Chaetae in a pair of ventrolateral bundles are present at segments two to nine in the first ring of each segment. Three bilimbate chaetae with whip-like extensions are present in the second segment in each bundle. All following segments with chaetae possess four bilimbate chaetae in each bundle. Gonochoristic; in males the paired spermioducts open ventrally in segment 10, in females the genital pores are located at the ventral boundary between the 10th and 11th segment. One or two vitellogenic oocytes can be observed at a time.

Habitat & Distribution: Specimens occur at beaches with medium-sized sand grains above the higher water level up to depth of 60 cm. Specimens are known only from the South African Atlantic coast.

Etymology. The species name minuta being Latin for small refers to the small size of this species in comparison to its two congeners.

Figures

FIGURE 4. Stygocapitella minuta. Langebaan, South Africa. SEM Images. (A) Entire specimen in ventral view, arrows point to segment borders. Note the pointed shape of the pygidium. (B) Enlargement of anterior end showing absence of forked chaetae in chaetal bundles. Arrows point to borders of achaetigerous anterior segment. (C) Enlargement of 1 st chaetal bundle; arrows point to chaetal follicles. (D) Detail of 2 nd group of chaetae. (E) Anterior end with opening of nuchal organ (no); arrow heads point to faintly visible sensory papillae, arrows point to segment borders.

FIGURE 5. Stygocapitella subterranea. Kiel Schilksee, Germany (type locality) SEM images. (A) Entire specimen in ventrolateral view, arrows point to segment borders. Note the rounded pygidium and the comparatively long 1 st segment; arrowhead points to opening of nuchal organ. (B) 1 st group of chaetae; whip-like extensions highly coiled and masked with detritus. (C) 2 nd chaetal bundle with 3 bilimbate and 2 forked chaetae. (D) 3 rd and following groups of chaetae comprise 2 bilimbate and two forked chaetae. (E) Frontal view of chaetae; each with separate follicle (arrrowheads); arrow points to forked chaeta with 2 spines. (F) Detail of forked chaeta with 3 spines, note surface of shaft composed of fine teeth. (G) Detail of bilimbate chaeta with teeth forming the surface. (H) Anterior end with sensory papillae (arrows) and opening of nuchal organ (arrowhead).

FIGURE 6. Stygocapitella australis sp. n.. Gnarabup beach (A, C, D, F), Sarge Bay (B, E, G); Australia. SEM images. (A) Entire female in ventrolateral view, arrows point to segment borders, arrowhead to female opening, nuchal organ (no). Note rounded pygidium and the comparatively long 1 st segment. (B) Male individual. (C) Anterior end of specimen in A; arrows point to borders of peristomium. Inset: enlargement of opening of nuchal organ, note cilia reaching the surface, scale bar: 1 µm. (D) Posterior end of female, arrows point to borders of achaetigerous segments; arrowhead to female opening in the furrow between chaetiger 9 and chaetiger 10. (E) 1 st group of chaetae comprising 2 bilimbate with whip-like extensions, 2 forked and 1 bilimbate chaeta. (F) 2 nd chaetal bundle with 2 bilimbate and 2 forked chaetae; each chaeta arising from separate follicle (arrowheads); arrow points to forked chaeta with 4 spines. (G) Detail of forked chaetae with 6 spines.

FIGURE 7. Comparison of chaetal patterns in the three species. Schematic representations of chaetae after SEM observations. All bundles shown in same orientation, left chaetae, ventral view; e. g., chaetae with extensions facing laterally.

FIGURE 8. Schematic drawings of holotypes or neotype of recognized Stygocapitella species. (A) Stygocapitella australis. (B) Stygocapitella subterranea. (C) Stygocapitella minuta. After light microscopic observations. Besides chaetal patterns, gut system and genital organs are shown. Segment borders in part masked by additional annuli; nervous system and nephridia not shown.